Why I Am Getting Error Due To Virtual Function ?

class Base
{
private:
    int m_age;
protected:
    int m_rank;
public:

    Base() { cout <<"Base created"<<endl;}

    //virtual // Ensures to invoke actual object destructor
    ~Base() { cout<<"Base destroyed"<<endl;}

    virtual void DisplayAction();
};


class Derived1 : public Base
{
public:
    Derived1()
    {
        cout << "Derived1 created" << endl;
    }

    ~Derived1()
    {
        cout << "Derived1 destroyed" << endl;
    }
    //void setage(int m){ m_age=m;}
    void setrank(int m){ m_rank=m;}
    void DisplayAction(){cout <<" rank= "<<m_rank;}

};